Early work demonstrated that 2-Butoxyethanol (BE) causes acute hemolytic anemia in rats and that metabolic activation of BE to butoxyacetic acid (BAA) is a prerequisite for the development of anemia. In an attempt to assess the potential health risks of humans exposed to BE, studies were designed to determine the in vitro effect of BAA on RBCs from 10 mammalian species. Blood samples from each mammalian species were incubated with BAA at a concentration of 0, 1, or 2 mM and kept at 37oC in a gently shaking water bath. Complete blood counts were measured at 0, 1, 2 and 4 hr. BAA caused a time- and concentration-dependent increase in MCV and HCT (followed by hemolysis in certain species), in rats, mice, hamsters, rabbits, and baboons. In contrast, blood from pigs, dogs, cats, guinea pigs, and humans was minimally affected by BAA. These results were confirmed in guinea pigs and rats in vivo. Gavage administration of 250 mg BE/kg to rats resulted in increased MCV and HCT followed by hemolysis. Identical treatment with BE resulted in no significant change in these parameters in guinea pigs.